1. Field of the Invention
The present invention relates to a terminal structure of a straight terminal such as a wide terminal for conducting a large current to be attached to a printed circuit board for an electronic control unit (ECU) or the like by soldering. Particularly, the invention relates to a holding structure and a heat dissipating structure thereof.
2. Description of the Related Arts
As a terminal holding structure of this type, one disclosed in JP-A-2000-68622 shown in FIGS. 20A and 20B is known. In this holding structure, a pair of upper and lower projecting portions 2 and 3 jutting out laterally with an interval corresponding to the thickness of a printed circuit board 5 therebetween are provided at a proximal portion of a plate-like straight terminal 1, as shown in FIGS. 20A and 20B.
Further, when the terminal 1 is inserted into an attaching hole 6 of the printed circuit board 5, the lower projecting portion 3 jutting out from both lateral sides of the proximal portion of the terminal 1 is inserted through a pair of semicircular slits 6a formed in an inner peripheral surface of the attaching hole 6 at positions opposing each other in the diametrical direction of the attaching hole 6, and the pair of projecting portions 2 and 3 are engaged with peripheral edge portions of the attaching hole 6 by rotating the terminal 1 by a predetermined angle. In the state in which the printed circuit board 5 is clamped by the pair of projecting portions 2 and 3 of this terminal 1, the proximal portion of the terminal 1 and a land portion 7 formed around the attaching hole 6 of the printed circuit board 5 are soldered so as to mount the terminal 1 in a state of being set vertically upright on the printed circuit board 5. This soldered portion (solder fillet) is denoted by reference numeral 8.
However, with the above-described conventional structure for holding the terminal 1 on the printed circuit board 5, since soldering is effected in such a manner as to completely cover the pair of projecting portions 2 and 3 of the terminal 1 for clamping the printed circuit board 5 (i.e., the distance between each of the pair of projecting portions 2 and 3 of the terminal 1 and the soldered portion 8 is very small), when an electric component such as an external connector is attached to or detached from the terminal 1, a large mechanical stress is directly applied to the soldered portion 8 from the vertical direction through the pair of projecting portions 2 and 3 of the terminal 1. Hence, a solder crack has been liable to occur in the soldered portion 8. In addition, a large thermal stress is directly applied to the soldered portion 8 through the pair of projecting portions 2 and 3 of the terminal 1 due to the environmental heat in the surroundings and the heat generated by such as the self heating of an electronic component including a fuse or a relay connected to the terminal 1. Hence, a solder crack has been liable to occur in the soldered portion 8. Furthermore, since the structure adopted is such that the land portion 7 on the printed circuit board 5 is clamped by the pair of projecting portions 2 and 3 of the terminal 1, the land portion 7 has been liable to be damaged by the pair of projecting portions 2 and 3 of the terminal 1.
Another terminal structures of related art are shown in FIGS. 21A, 21B and FIG. 22. In the holding structure shown as in FIG. 21A, a soldering portion 102 at a lower end of a plate-like wide terminal 101 for conducting a large current is inserted into a connecting hole 106 formed in a printed circuit board 105, and the soldering portion 102 of the terminal 101 is fixed by soldering to a land portion 107 formed around the connecting hole 106 on the lower surface of the printed circuit board 105. As shown in FIG. 21B, the land portion 107 is formed in a substantially annular elliptical shape having an elliptical elongated hole 107a in its center. A soldered portion (solder fillet) is denoted by reference numeral 108 in FIG. 21A.
In the terminal structure shown in FIG. 22, a soldering portion 202 at a lower end of a straight terminal 201 is inserted into a connecting hole 206 formed in a printed circuit board 205, and the soldering portion 202 of the terminal 201 is fixed by soldering to a land portion 207 formed around the connecting hole 206 on the lower surface of the printed circuit board 205. A heat generating component 204 such as a fuse or a relay is detachably connected to an upper end 203 of the terminal 201. A soldered portion (solder fillet) is denoted by reference numeral 208 in FIG. 22.
However, with the above-described conventional structures for attaching the terminals 101, 201 to the printed circuit boards 105, 205, when a large current is conducted in a state in which the heat generating component 104 (204) such as the fuse or the relay is fitted to the upper end 103 (203) of the terminal 102 (202), and the soldering portion 102 (202) of the terminal 101 (201) is soldered to the land portion 107 (207) of the circuit board 105 (205), in a case where the component body of the heat generating component and fitting portions of the heat generating component 104 (204) and the upper end 103 (203) of the terminal 101 (201) have generated heat, the heat is directly transmitted to the soldered portion 108 (208) through the terminal 101 (201) in the form of a thermal stress. Hence, a solder crack has been liable to occur in the soldered portion 108 (208).
Further, in the holding structure of the terminal 101, since the land portion 107 which is formed on the lower surface of the printed circuit board 105 has in its center the elliptical elongated hole 107a, the durability of the land portion 107 has been inferior and liable to be damaged. Hence, the fabrication cost of the printed circuit board 105 has been high to improve the quality.
In the holding structure of the terminal 201, when the heat generating component 204 is attached to or detached from the upper end 203 of the terminal 201, a large mechanical stress is directly applied from the vertical direction to the soldered portion 208 through the soldering portion 202 of the terminal 201. Hence, a solder crack has been liable to occur in the soldered portion 208.